Embodiments of the present disclosure relate to a Bits Per Inch (BPI) control method for a disk and a hard disk drive (HDD) controlled by the same, and particularly, to a BPI control method for a disk capable of increasing a capacity and enhancing reliability by differently controlling BPI of a disk in a circumferential direction, and an HDD controlled by the same.
A hard disk drive (HDD), one of data storage devices contributes to an operation of a computer system by reading data recorded onto a disk or by recording user data onto a disk by a magnetic head.
Due to recent trends of the HDD, such as a high capacity, high density and miniaturization, a more sophisticated mechanism is required.
A recording medium of the HDD, a disk has a magnetic recording layer recorded on its surface by a thin film application method. Here, an expected capacity may become deficient and reliability may be degraded due to micro non-uniformity occurring on the disk surface. The non-uniformity may mean a physical/chemical flat degree of the disk surface.
FIG. 1 illustrates a BPI control graph with respect to a disk in accordance with the conventional art, and FIG. 2 is a graph schematically illustrating a correlation between a disk and BPI.
Referring to FIG. 1, BPI of an HDD being presented to the market is differently controlled with consideration of an angular speed in a radial direction (a). That is, the HDD is controlled so that its BPI can increase towards an outer radius (OR) longer than an inner radius (IR).
In the conventional art, the HDD is controlled to have the same BPI since BPI control in a circumferential direction (b), a cylinder direction of the disk is complicated or difficult. As a result, an expected capacity may become deficient and reliability may be degraded due to micro non-uniformity occurring on the disk surface.
Referring to FIG. 2, the disk surface onto which a magnetic recording layer is recorded by a thin film application method cannot have an ideal complete planar surface. According to a flat degree, the disk surface may have a position (D1) of high read/write performance, and a position (D2) of low read/write performance. That is, the disk has a non-uniform surface (P) relatively lower than the other surface.
Such phenomenon always occurs while manufacturing a disk. As shown in FIG. 2, if the HDD is controlled to have the same BPI in a circumferential direction (b) without consideration of such phenomenon, an expected capacity may become deficient and reliability may be degraded due to the non-uniform surface (P).
To solve such problems, BPI may be decreased, which results in a large size of data. If a data size increases, an error rate during a read operation is reduced, but a capacity is lowered.
On the contrary, if BPI is increased, a data size decreases thus to increase a capacity. However, in this case, an error rate during a read operation increases.
FIG. 3 is a graph illustrating Over Write (OW) on the disk surface in a circumferential direction (Media OW), and a read/write error rate on a corresponding position.
Referring to FIG. 3, the OW on the disk surface, and a bit error rate (BER) on a corresponding position change in proportion to each other.
Such phenomenon may occur due to a non-uniform degree on the disk surface. This may cause degraded reliability that a reading or writing operation cannot be successfully performed on a position having low OW.
In order to solve such degraded reliability, the entire BPI applied to the HDD may be lowered, or the OW on the disk surface may be increased. In this case, the HDD may have a decreased capacity, and may have degraded productivity due to a reduced yield.
As aforementioned, the HDD has different read/write performance due to non-uniformity on the disk surface. However, if the HDD is controlled to have the same BPI on the surface in a circumferential direction like in the conventional art, a capacity may become deficient and reliability may be degraded. Therefore, a new solution is absolutely required.